1. Field of the Invention
The present invention is directed to a connector device for a sensor or actuator, particularly for surface antennas in magnetic resonance systems, of the type composed of two terminal elements releasably connected to one another, a first of those terminal elements includes a first electrical conductor that is connected to the sensor or actuator and a second of these terminal elements includes a second electrical conductor that is connectible to an evaluation unit, whereby the first and second electrical conductors are coil systems that enable signal transmission by inductive coupling given a connection of the two terminal elements.
2. Description of the Prior Art
The acquisition and forwarding of sensor signals in a radio-frequency system, such as, for example, a magnetic resonance apparatus, makes high demands as to immunity to interference and dependability of the signal transmission. Magnetic resonance tomography is a known technique for acquiring images of the inside of the body of a living examination subject. A magnetic resonance tomography apparatus has a basic field magnet for generating a uniform magnetic field for the polarization of the atomic nuclei in the body to be examined, a number of gradient coils for the location coding of the magnetic resonance signals as well as one or more radio-frequency transmission antennas that emit radio-frequency pulses for triggering the magnetic resonance signals into the body to be examined. The magnetic resonance signals that are generated are acquired via a sensor and are supplied to an evaluation unit for the calculation of the magnetic resonance images. Either the radio-frequency transmission antenna utilized for the excitation of the magnetic resonance signals, referred to as the whole body antenna, or one or more radio-frequency reception antennas not rigidly connected to the magnetic resonance tomography apparatus, referred to as surface antennas, are utilized as sensors. Magnetic resonance images having a better signal-to-noise ratio can be registered with a surface antenna. It is brought close to the body region to be examined and is connected via a connecting cable to the evaluation unit of the magnetic resonance tomography apparatus.
The connection between the surface antenna and the evaluation unit is currently designed as a galvanic plug-type connector wherein one of the two terminal elements, that are releasably connectable to one another, is connected to the surface antenna and the other is connected to the evaluation unit. These plug-type connectors have the advantage of a flexible manipulation, since the surface antennas can be removed in a simple way and replaced by other surface antennas and can be connected to the evaluation unit via the plug-type connector.
One disadvantage of the known plug-type connectors, however, is that the electrical contacts can be only inadequately disinfected due to their being freely accessible. In the medical sector, however, a regular disinfection of the examination apparatus is important. Further, the problem arises given the known plug-type connectors that undesired sheath waves propagate on the leads, which may lead to a heating of adjacent body tissue that is unpleasant for the patient.
German PS 3616389 discloses a proximity switch acting in non-contacting fashion in a different technical field that is composed of a signal-processing part, a main part and a signal-acquiring sensor part that is pluggable to the main part. The signal and energy transmission between the sensor part and the main part given this proximity switch ensues via inductive coupling on the basis of integrated core coils that lie directly opposite one another when the two parts enter into a plug-type connection.
The same principle of signal transmission by inductive coupling is also utilized in a bio-magnetometer disclosed in German Translation 69029375. With this bio-magnetometer, extremely small magnetic fields are measured, these being generated, for example, by the brain of a patient. The bio-magnetometer contains a superconducting, magnetic pick-coil that is connected to a highly sensitive magnetic signal detector, a SQUID. The entire system is accommodated in Dewar vessels for producing the temperatures required for the super-conduction. The publication proposes that the pick-up coil and the magnetic signal detector be arranged in two different Dewar vessels that are detachably connected to one another. For the signal transmission, transmission coils are situated in each Dewar vessel that are fashioned and arranged such that they are coaxially thrust inside one another given a connection between the two Dewar vessels.
The principle of signal transmission by inductive coupling utilized in these two publications, however, does not seem suitable for operation in a magnetic resonance system, since the transmission coils are exposed to high radio-frequency fields therein that disturb the signal transmission and are also influenced by it.
An object of the present invention is to provide a connector device for a sensor or actuator, particularly for a surface antenna in a magnetic resonance system, that avoids the above disadvantages and can be unproblemmatically disinfected.
The object is achieved in a connector device according to the invention that is composed of two terminal elements releasably connectible to one another, with a first of these terminal elements includes a first electrical conductor that is connected to the sensor or actuator and a second of these terminal elements includes a second electrical conductor that is connectible to an evaluation unit. The first and second electrical conductor are coil systems that enable signal transmission by inductive coupling where the two terminal elements are connected to one another. Each of the coil systems is formed of at least two series-connected coils that have oppositely directed windings and are dimensioned such that the sum of voltages induced in the coils by a uniform electromagnetic field yields zero for each of the coil systems.
As a result of this fashioning of the connector device, the signals received by the sensor or sent to the actuator are not galvanically transmitted but are transmitted by inductive coupling between the two terminal elements of the connector device, for example of a plug-type connector. This design enables the complete hermetic sealing of the sensor or actuator with the first terminal element, so that no electrical conductors are exposed. This is especially advantageous for surface antennas that are potentially exposed to body fluids such as, for example, a prostate coil. With the inventive connector device, surface antennas that can be completely disinfected and sterilized can be achieved. In the same way, the second terminal element of the connector device, which may come into contact with the patient, can be completely hermetically sealed. As a result of a complete encapsulation, all disinfection measures can be unproblemmatically implemented, so that the inventive connector device is excellently suited for utilization in the medical field.
In the inventive connector device, reduction emission from the coupled connection, and the influence of external radio-frequency fields, are achieved by a special design of the two coil systems in the terminal elements. Each of the coil systems is formed of at least two series-connected coils that have oppositely directed windings and are dimensioned such that the sum of currents induced in the coils due to a uniform electromagnetic field yields zero for each of the coil systems. This is achieved by a suitable selection of the area and the number of turns in conjunction with the direction of the winding of the individual coils. The sum of the product of area and number of turns for all individual coils of each coil system must yield approximately zero, whereby oppositely directed numbers of turns are distinguished by opposite operational signs. Only as a result of this design is the disturbance-free utilization of the connector element enabled in radio-frequency fields as particularly occur in magnetic resonance systems.
Each coil system is preferably composed of two series-connected coils with the same dimensioning, i.e. same area and same number of turns, that are wound oppositely (in opposite senses). As a result of this design, the fields generated by the oppositely directed coils of the respective coil systems cancel nearly completely at the exterior of the connector. The fields of the coils are of adequate strength only in the close proximity region wherein the inductive coupling between the coil systems ensues.
Another advantage of the inventive connector device is that, given the connection via the connector device of one or more surface coils to the evaluation unit, significantly reduced leakage currents occur via the connecting line. By suppressing the common mode, moreover, the sheath waves are also suppressed, so that no heating that is unpleasant for the patient occurs given contact with the connecting cable.
In contrast to a conventional galvanic plug-type connectors, no wear of electrical contacts occurs given the inventive connector device.
The invention is explained below with reference to employment wherein the connector device produces a connection between a surface antenna fashioned as coil and the evaluation unit of a magnetic resonance system. Of course, other types of sensors or actuators can be connected to an evaluation unit with the present connector device. Examples are sensors for measuring blood pressure, temperature or a ECG or actuators for generating sound or electrical stimulation The structure of the connector device is the same as given employment with the surface antenna.
The connector device is composed of two terminals elements releasably connected to one another that are preferably designed as plug-type connectors. Each of the terminal elements contains a coil system. The coil system of one of the terminal elements is electrically connected to the surface coil either directly or via intermediate elements, for example a modulation circuit. The coil system of the other terminal element is connected or at least connectible to the evaluation unit via a connecting cable. For example, a conventional galvanic plug-type connector for the connection to the evaluation unit can be provided at that end of the connecting cable not connected to the coil system. The connecting cable, however, alternatively can be directly connected to the evaluation unit, i.e. non-releasably.
The terminal elements themselves are composed of an electrically non-conductive material, preferably a plastic. The same materials as are utilized for conventional galvanic plug-type connectors in the present field can be employed as materials in the inventive connector.
The two terminal elements must be fashioned such that they enable a releasable connection. This can ensue by means of different mechanical mechanisms that are known to a those skilled in the art in the field of releasable mechanical connections.
The two terminal elements are preferably fashioned as plug-type connectors; for example, one terminal element can represent a socket and the other can represent the appertaining plug.
In a preferred embodiment of the inventive connector device, the coil systems are fashioned and arranged in the terminal elements such that they are coaxially thrust inside one another when the releasable connection between the terminal elements is produced. This means that the coils of the one terminal element surround the coils of the other terminal element in the connection. In this way, an optimum inductive coupling is achieved between the two coil systems. The terminal elements, of course, must be fashioned such by appropriate shaping so that they enable this mutual positioning of the coil systems as a result of the connection.
For employment of the inventive connector device in a radio-frequency environment, an especially low emission toward the exterior and a low sensitivity relative to external RF fields must be insured. This is additionally supported in an embodiment of the inventive connector device wherein the coil system that is located at the outside in the coupled state is additionally surrounded by a shielding winding. This shielding winding is fashioned around the outer circumference of that coil system in its terminal element. Since the coupling to the other (inner) coil system of the other terminal element ensues within this shielding winding, the signal transmission is not degraded and the two coil systems are shielded from the environment.
In an embodiment of the inventive connector device, a loss-free matching network is additionally provided for the compensation of insertion losses in the inductive coupling, this being connected to the two inductances in the terminal elements.
In addition to the signal transmission from the surface coil to the evaluation unit, the surface coil or electrical components connected thereto can be charged with control signals or be supplied with energy via the connector device. To this end, one or more modulation circuits together with one or more frequency generators are arranged at the side of the second terminal element, for modulating additional control signals and/or signals for generating a supply voltage onto one or more carrier frequencies and for transmitting the modulated signal to the surface coil arrangement. At the other side of the surface coil arrangement, i.e., the first terminal element, at least one demodulation circuit is provided that extracts the corresponding control signals or for the voltage supply signals from the carrier frequency signal and makes the demodulated signal available to the electrical components.